The present invention relates to a method for actively influencing noise, in particular in a motor vehicle. The invention also relates to a corresponding system and the use thereof in a motor vehicle.
Systems for actively influencing noise, which are also called ANC systems (active noise control), are used, for example, in a passenger compartment of a motor vehicle to reduce the noise level of a source of disturbance, for example from the engine, by introducing controlled acoustic signals. In this active compensation, the noise is reduced by superimposition of additional vibrations, so-called anti-noise. It is also possible to amplify any desired harmonics and/or the fundamental tone of the primary noise by the controlled introduction of secondary sound. Ordinarily, harmonic tone sequences are perceived as pleasant, for example. By predetermined suppression of individual frequencies of the engine noise and amplifying other frequencies, a perceived engine noise can be configured in a predetermined manner, for example. This is then also referred to as sound design.
Compensation sound is taken below to mean secondary sound that is introduced additionally to the noise and that can act in an amplifying manner and also in an attenuating manner at certain sound frequencies.
The same principle emerges in the compensation of solid-borne sound, with counter-vibrations being introduced in a solid body by means of actuators and these counter-vibrations causing a reduction in noise or a change in the noise.
Generally, the sound sources or vibration sources are substantially periodic sound sources. The excitation frequency of the noise source which is derived from the periodicity is in this case used as an input variable for an adaptive control of the noise reduction system. If this variable which is characteristic of the respective noise source changes with respect to time, an adaptive controller of the noise reduction system carries out a corresponding adaptation in the compensation noise introduction.
An adaptive control for active noise reduction is known, for example, from DE 196 32 230 C2. A reference signal generator is provided there, which detects an engine speed and generates an electronic reference signal having information about the engine speed. This may, for example, be a pulse signal, which is guided via signal lines to a sine-wave generator provided in the noise reduction system. In the motor vehicle, a corresponding reference signal may also be derived from the ignition coil signal, which is directly linked with the engine speed and therefore the acoustic excitation frequency of the engine.
It is necessary in active noise reduction systems to hold in readiness the corresponding excitation frequency or an equivalent reference signal for the activation of the actuators or compensation loudspeakers as continuously with respect to time as possible. In noise reduction systems according to the prior art, a measurement sensor generally used close to the engine and providing a corresponding reference signal to the actual controller of the noise reduction system is therefore provided. In this case, the noise reduction system is generally arranged in the passenger compartment, so long signal paths and corresponding cabling are necessary.
Because of progressing automation and the integration of various control tasks in modern systems in a digital manner, analogue time-continuous monitoring signals are scarcely still available. In modern motor vehicles, the data communication takes place, for example, by means of digital bus systems, such as, for example the CAN bus (Controller Area Network Bus). Real time data communication is no longer possible in such asynchronous serial bus systems. To display the engine speed in the dashboards of a motor vehicle, a supply rate of only 10 times per second is sufficient, for example.
Typically, a plurality of bus systems is provided in current motor vehicles. A first high speed bus is provided in this case in the engine compartment which networks the engine control and has a supply period for the engine speed in the order of magnitude of 10 to 20 milliseconds. A second slower data bus, which is coupled via a gateway to the high speed bus, is used to network control apparatuses for comfort and interior functions of the motor vehicle, such as, for example, speedometer, rev counter etc.
The important reference variable of the engine speed for a system for actively influencing noise is therefore only available, however, at a lower supply rate of about 10 times per second, in other words every 100 milliseconds on the slower data bus, which is provided in the interior of the motor vehicle. The reference variable which is only present in a very rough time-discrete manner, such as the engine speed, makes operation of the active system in the passenger compartment more difficult, in particular when accelerating and braking the engine.
It is therefore an object of the present invention to provide a reliable method for influencing noise. It is an object of the invention to provide a system for actively influencing noise.